Income Taxes--Components of Deferred Tax Assets and Liabilities (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013	Dec. 31, 2012
Deferred Income Tax Assets And Liabilities [Line Items]
Asset retirement obligations	$ 8,777	$ 8,496
Accrued expenses, allowance and other	14,508	10,129
Derivative instruments	129	0
Net operating loss carryforwards - Federal	124,855	153,709
Net operating loss carryforwards - State	13,350	16,339
Statutory depletion carryforwards	2,867	2,242
Alternative minimum tax credit carryforwards	308	308
Deferred tax assets, gross	164,794	191,223
Less valuation allowance	(10,385)	(11,858)
Deferred tax asset	154,409	179,365
Derivative instruments	0	(32,438)
Property and equipment	(206,799)	(181,489)
Inventories	(1,205)	(1,211)
Deferred tax liability	(208,004)	(215,138)
Net deferred tax liability	(53,595)	(35,773)
Net current deferred tax asset	9,260	0
Net current deferred tax liability	0	(26,872)
Long-term deferred tax liability	$ (62,855)	$ (8,901)